1. Field of the Invention
The present invention relates to an apparatus for manufacturing electrical device packages. More particularly, the invention relates to an apparatus for dispensing a liquid encapsulant to encapsulate a semiconductor chip that is attached to a tape.
2. Description of the Related Art
In a typical process for fabricating a plastic semiconductor package, a semiconductor chip after being attached and wire-boned to a lead frame is encapsulated with a molding compound by transfermolding. However, other packaging process can employ different encapsulation methods. For example, a micro ball grid array (.mu.BGA) package, which includes a tape instead of a leadframe of the plastic package, is encapsulated by a liquid encapsulant coating process.
The tape typically has windows exposing parts of the beam leads for connection to the semiconductor chip. A fabrication method, which employs the tape with windows, is described below. A typical assembly process for assembling a .mu.BGA package begins with providing a tape made of, for example, polyimide, and having windows and metal beam leads across the windows. A semiconductor chip is attached to the tape using an adhesive, and the beam leads are connected to bonding pads on the chip through the windows. Then the windows are filled with an encapsulant to protect the chip and the electrical connections.
FIG. 1 is a schematic diagram showing a conventional reel-to-reel dispensing apparatus 100 for filling the windows with an encapsulant. Apparatus 100 includes: a dispensing station 40 for coating a liquid encapsulant on a tape 10 to which a semiconductor chips 11 are attached; a reel-to-reel handling track 60 for moving tape 10 at dispensing station 40; a tape feed station 20 for feeding tape 10; and a tape take-up station 70 for unloading tape 10 from dispensing station 40 after the coating process. The structure of apparatus 100 will be explained based on the order of the movement of tape 10.
A tape feed reel 22 of tape 10 is loaded into tape feed station 20. A protection tape 30 which is wound with tape 10 in reel 22 to protect chips 11 is removed from the reel as tape 10 is supplied to dispensing station 40. When removed, protection tape 30 is wound to a protection tape take-up reel 26, while tape 10 moves to a support plate 50 in dispensing station 40. In dispensing station 40, a syringe 42 above support plate 50 dispenses a liquid encapsulant through a needle 44 to an upper surface 12 (FIG. 2) of tape 10, which includes chips 11. An actuator 46 coupled to syringe 42 controls the movement of syringe 42. Tape 10 is then transferred to tape take-up station 70 which winds tape 10 on a reel 72. At the same time, a protection tape 80 for protecting chips 11 on tape 10 is wound as an interleaf. Reel-to-reel handling track 60 controls the movement of tape 10 from tape feed station 20 to tape take-up station 70.
Dispensing of the liquid encapsulant on the top of tape 10 is further described with reference to FIG. 2. In FIG. 2, chip 11 is attached to tape 10 by an elastomer adhesive 18, and beam leads 16 electrically connect chip 11 to tape 10 at windows 14. For encapsulation, tape 10 is placed on support plate 50. A suction port 52 connected to a vacuum pump (not shown) holds tape 10 to support table 50.
Then, syringe 42 (FIG. 1) dispenses a liquid encapsulant 47 along periphery of chip 11 to protect the electrical connection area between chip 11 and beam leads 16. When dispensed, liquid encapsulant 47 fills windows 14 (47b), covers the periphery of chip 11 (47a), and undesirably runs out through a gap between tape 10 and support table 50 (47c). This may eventually contaminate support plate 50 and adversely affect dispensing encapsulant on following tapes.
To stop the encapsulant from running into the gap, several methods have been proposed. Two representative examples are depicted in FIG. 3 and FIG. 4. FIG. 3 shows a tape 10 covered with a photo solder resist (PSR) film 90, which can be removed by etching after dispensing, and FIG. 4 shows a piece of tape 10 temporarily held on a magazine substrate 94.
With reference to FIG. 3, tape 10 having windows 14 and sprocket holes 19 has PSR film 90 formed on the bottom surface of tape 10 before the encapsulant coating step. PSR film 90 can prevent the liquid encapsulant from running onto support table 50 (FIG. 2). After the encapsulant is cured, etching can remove PSR film 90.
With reference to FIG. 4, tape 10, which is cut to size, is placed on a magazine substrate 94. Magazine substrate 94 has a surrounding lip that prevents the liquid encapsulant from running onto support table 50 (FIG. 2).
However, the method of FIG. 3 requires costly processing steps including forming PSR film 90 on the bottom of tape 10 before the encapsulant coating step, and partly removing PSR film 90 to expose windows 14 and solder ball pads (not shown). The method of FIG. 4 reduces manufacturing efficiency by requiring an addition of tape cutting step, and because a batch-type process using tape strips is less efficient than a reel-to-reel process.